tests/test-dirstate-backup.t

py3: port tinyproxy.py to work with Python 3

There were various str/bytes mismatches in the code. This caused
the proxy server to misbehave at run-time. The manifestation
was typically premature socket disconnect from the perspective
of the client.

Differential Revision: https://phab.mercurial-scm.org/D5951

Set up

  $ hg init repo
  $ cd repo

Try to import an empty patch

  $ hg import --no-commit - <<EOF
  > EOF
  applying patch from stdin
  abort: stdin: no diffs found
  [255]

No dirstate backups are left behind

  $ ls .hg/dirstate* | sort
  .hg/dirstate